Piezoceramic composition, piezoceramic body comprising said composition and a method for producing said composition and said body

ABSTRACT

The invention relates to a piezoceramic composition with the general empirical formula Pb 1-a RE b Zr x Ti y TR z O 3 , in which RE represents a rare-earth element, selected from a group comprising europium, gadolinium, lanthanum, neodymium, praseodymium, promethium and/or samarium, with a rare-earth element fraction b, TR represents at least one transition metal, selected from the group comprising chromium, iron and/or manganese, with a transition metal valency W&lt;SB&gt;TR&lt;/SB&gt;and a transition metal fraction z and whereby the following interrelation is valid: z&gt;b/(4−W&lt;SB&gt;TR&lt;/SB&gt;). Homogenous PZT crystals with a maximum particle size are obtained even at low sintering temperatures by a non-stoichiometric dosing ratio of transition metal dosage to rare-earth element dosage. By varying the dosages, the piezoelectric characteristics of a PZT ceramic with said composition can be modified from those of a classic soft PZT to those of a classic hard PZT. The piezoceramic body is for example a monolithic, multi-layer piezoactuator, which can be used for multiple injections in the engine of a motor vehicle, as a result of a high d 33  coefficient and low internal dissipation in the high-level signal range.

The invention relates to a piezoceramic composition in the form of alead zirconate titanate (Pb(Ti, Zr)O₃, PZT). In addition a piezoceramicbody with the composition as well as a method of producing saidcomposition and a method of producing said body are specified.

Lead zirconate titanate is a perovskite in which the A-sites of theperovskite are occupied by bivalent lead (Pb²,) and the B-sites of theperovskite by quadrivalent Zirconium (Zr⁴⁺) and quadrivalent titanium(Ti⁴⁺). To influence an electrical or piezoelectrical property such aspermittivity, coupling factor or piezoelectric charging constant (forexample d₃₃ coefficient) the composition is usually doped.

With what is known as a hard PZT, lower-value cations are incorporatedat the A- or B-site of the perovskite. These cations are referred to ashardener doping. For a classical hard PZT the result of this type ofdoping is a relatively low dissipation factor tg δ and thereby a highmechanical quality factor Q_(m). The mechanical quality factor Q_(m)amounts to 1000 for example. The high quality factor means that aninternal dissipation which occurs with an electrical activation of acomponent with the hard PZT is low. However the d₃₃ coefficient of thehard PZT is relatively low. Hard PZT is thus not suitable for the typeof application in which the greatest possible piezoelectrically-induceddeflection is to be achieved. Hard PZT is thus rarely used in apiezoelectric actuator or in a piezoelectric bending converter.

With what is known as a soft PZT on the other hand, higher-value cationsare built in at the A- or B-site of the perovskite. These cations arereferred to a softener doping. This type of soft PZT is for exampleknown from WO 97/40537, in which a small proportion of trivalentneodymium (Nd³⁺) occupies the A-site of the perovskitic PZT. The generalmolecular formula of the piezoceramic composition of the soft PZT isPb_(0, 98)Nd_(0, 02)Zr_(0, 54)Ti_(0, 46)O₃. The softener doping meansthat a classic soft PZT is identified by a relatively high d₃₃coefficient both in the low-value signal range (with field strengths ofa few V/mm) and also in the high-value signal range (with fieldstrengths of a few kV/mm). Soft PZT is thus suitable for use inactuators or bending converters. The disadvantage of this is that thedissipation factor tg δ is very high and thus a mechanical qualityfactor Q_(m) is very low. The mechanical quality factor Q_(m) amounts to80 for example. In operation of a component with soft PZT a highinternal dissipation therefore occurs, especially in the high-valuesignal area and this can lead to an undesired heating up of thecomponent.

The object of the present invention is to specify a piezoceramiccomposition which exhibits both a high mechanical quality factor Q_(m)and also a large d₃₃ coefficient.

The object is achieved by a piezoceramic composition with the generalmolecular formula Pb_(1-a)RE_(b)Zr_(x)Ti_(y)TR_(Z)O₃, in which RE is atleast a selected rare earth element from the group europium, gadolinium,lanthanum, neodymium, praseodymium, promethium and/or samarium with arare earth metal proportion b, TR is at least one transition metalselected from the group chromium, iron and/or manganese with atransition metal valency W_(TR) and a transition metal proportion z andthe following relationship applies. z>b/(4−W_(TR))

To achieve the object a method for producing the piezoceramiccomposition is thus to be specified in which a maximum particle growthof the piezoceramic composition is determined for a specific sintertemperature.

In addition, to achieve the object, a piezoceramic body with thepiezoceramic composition and a method for manufacturing the piezoceramicbody will be specified. The method features the following steps:Provision of a green body with the piezoceramic composition andsintering of the green body to the piezoceramic body.

The rare earth metal RE and the transition metal TR are dopings of thePZT. In this case the PZT can be doped with a number of rare earthmetals RE_(I) with corresponding rare earth metal proportions b_(I).Thus the rare earth proportion b can represent a sum of a number of rareearth metal proportions b_(I). Likewise the PZT can also be doped with anumber of transition metals TR_(j) with corresponding transition metalproportions z_(j). The transition metal proportion z can thus be a sumof the transition metal proportions z_(j).

The possible rare earth metals (softener dopings) are selected so that,by comparison with Pb²⁺, they exhibit a similar ion radius. This leadsto these rare earth metals primarily taking up the A-sites of theperovskitic PZT. The rare earth metals are preferably present astrivalent cations RE³⁺, so that the A-sites are partly occupied byhigher dopings by comparison with Pb²⁺.

The possible transition metals (hardener dopings) are selected such thatbecause of their ion radii, they primarily occupy the B-sites of theperovskitic PZTs. The rare earth metals preferably occur here with avalency of +2 or +3 so that the B-sites are primarily occupied bylower-valency dopings by comparison with Ti⁴⁺ and Zr⁴⁺.

Of particular importance, in addition to the explicit choice of thedopings, is the ratio of softener to hardener doping, expressed by therelationship of the transition metal proportion z, the deviation of thevalency W_(TR) from +4 (the valency of titanium and zirconium at theB-sites) and of the rare earth metal proportion b. For the inventivelyimportant relationship softener and hardener doping are added to eachother non-stoichiometrically. Softener and hardener dopings would bemixed stoichiometrically if the following relationship were to apply:z=b/(4−W_(TR)). Through the non-stoichiometric ratio a change in chargein the PZT brought about by the softener doping is overcompensated forby the hardener doping. With a hardener doping with trivalent iron(Fe³⁺) or trivalent chromium (Cr³⁺) for example more trivalenttransition metal will be added than would be necessary as a result ofthe rare earth metal proportion and deviation of the valency of the rareearth metal (+3) from the valency of the lead (+2) (Z_(Fe)>b orZ_(cr)>b) . The same applies for a hardener doping with bivalentmanganese (Mn²⁺) (Z_(Mn)>b/2). A mixed doping of bivalent manganese andtrivalent iron for example produces the relationship forZ_(Fe)+2.z_(Mn)>b.

Surprisingly it has been shown that, for a non-stoichiometric ratio ofthe softener and the hardener doping to each other, PZT crystals areaccessible which exhibit a relatively large particle size. In this casePZT crystals with a particle diameter of far in excess of 1 μm areaccessible practically independent of the sinter temperature. Theparticle diameter of 1 μm is viewed as the critical minimum particlesize for PZT, above which PZT exhibits good and thereby technicallyusable piezoelectric properties. The large particle sizes are possibleby virtue of the fact that, based on the inventive relationship of thedopings, a maximum value particle growth of the PZT crystals can be set.With maximum particle growth almost no growth inhibitors occur as blanklocations of the A-sites or B-sites or local doping complexes. With theinventive doping relationship almost every inhibitor to particle growthis removed. The dopings are built in both in the thermodynamicequilibrium and also in the charging equilibrium at a given sintertemperature homogenously into a growing PZT crystal. The result is that,under given sinter conditions (for example sinter temperature or sinteratmosphere) the largest possible PZT crystals are obtained. The range ofmaximum particle growth is to be defined empirically. The approximaterelationship is as follows: (4.b)/(4−W_(TR))>z>b/(4−W_(TR)). Forexample, at a sinter temperature of 1050° C. the maximum particle growthof a piezoceramic composition with a neodymium proportion b_(Nd) of 2mol % with a manganese proportion Z_(Mn), of around 1.5 mol %. PZTcrystals with a particle diameter of up to 13 μm are obtained. Bycontrast a doping with iron instead of manganese, with an ironproportion z_(Fe) of around 4 mol %, leads to maximum particle growth,with PZT crystals with a particle diameter of up to 10 μm beingachievable. The result in the range of the maximum particle growth isrelatively large PZT crystals.

The larger the PZT crystals the larger is the d₃₃ coefficient which canbe achieved with these PZT crystals. Despite a relatively highproportion of hardener doping, a larger d₃₃-coefficient can be realizedin this way than is typical for soft PZT. As a result of the relativelyhigh proportion of hardener doping however it is possible by comparisonwith classical soft PZT to obtain a far dissipation factor tg δ. Thedissipation factor tg δ and thereby the mechanical quality factor Q_(m)which can be achieved can assume values which are typical of classicalhard PZT.

The value of the mechanical quality factor Q_(m) in particular is in arange from 50 up to and including 1800. It has been shown that theelectrical and piezoelectrical properties of the composition can betuned from those of a classic soft PZT through to the properties of aclassic hard PZT. The type of transition metal plays an important rolehere. A doping with manganese leads for example to an increased particlegrowth and simultaneously a reduction in the dissipation factor tg δ.These effects also occur with low manganese proportions. Thus a larged₃₃ coefficient (for example 550 pm/V for an activation of 2 kV/mm) canbe achieved at low internal dissipation.

A doping with iron results with only a slight deviation from thestoichiometric ratio of the rare earth metal and of the iron (Z_(Fe)=b)in an increased particle growth. But, unlike the doping with manganese,with the iron doping the dissipation factor tg δ only decreases with agreater deviation from the stoichiometric ratio. The deviation necessaryfor this amounts to 50% for example and lies within range of maximumparticle size. This means that here, up to a ratio of the proportion ofiron z_(Fe) to transition metal proportion b of 2 a larger d₃₃coefficient can be achieved at a high internal loss. Thus the hardenerdoping with iron makes a composition with piezoelectric propertiesaccessible which are typical of a classic soft PZT. With the maximumparticle size for example a soft PZT is produced for which thehigh-level signal d₃₃ coefficient of around 950 pm/V at 1 kV/mm, despitehardener doping, is still above the known values for a classic soft PZTwhich only exhibits one softener doping.

The method for producing the piezoceramic composition comprises in aparticular embodiment the following steps: Defining the rare earth metalproportion b, Defining the transition metal proportion z, sintering thepiezoceramic composition at the sinter temperature, determining aparticle size of the sintered piezoceramic composition and repeating thedefinition of the transition metal proportion z, of the sintering and ofthe determining of the particle size, with the transition metalproportion z being varied.

To set the desired relationship of the piezoceramic properties of aclassic hard PZT to those of a classic soft PZT a mixed doping ofmanganese and iron is used especially. Alternatively a mixture ofmanganese and chrome can also be used. For the mixed doping of manganeseand iron the transition metal iron with an iron proportion z_(Fe) andthe transition metal manganese with a manganese proportion Z_(Mn) isused, so that the ratio to z_(Fe)+2.z_(Mn), >b is produced and with thevariation of the manganese proportion Z_(Mn) essentially the dissipationfactor tg δ of the composition and with the variation of the ironproportion z_(Fe) essentially the maximum particle growth of thecomposition are set. Essentially this means that, with the transitionmetal proportions the dissipation factor tg δ of the iron doping and theparticle growth are only slightly influenced by the manganese doping.

For example, for a given rare earth metal doping with rare earth metalproportion b a manganese proportion Z_(Mn) is explicitly selected whichis lower than the manganese proportion which leads to the maximumparticle size. Then sufficient iron is doped in until the point ofmaximum particle size is determined. A charge equalization in the PZTwhich is triggered by the non-stoichiometric relationship of softenerand hardener dopings to each other is normally compensated for via emptypositions. The result of the formal non-stoichiometric composition ishowever that with maximum particle growth no compensation via emptypositions is necessary. At a given sinter temperature maximum particlegrowth takes place at an empirically determined ratio of transitionmetal proportion to rare earth metal proportion. With this ratio thecations are built into a practically defect-free perovskite by changingthe valency and/or A/B-site equilibriums.

In a further embodiment the following further relationship applies:x+y+z=1. Zirconium, titanium and the transition metal are preferablybuilt into the B-site of the perovskite. By changing the relationshipbetween the zirconium proportion x and the titanium proportion y, themorphotropic phase boundary necessary for the piezoelectric propertiesof the PZT of tetragonal and rhomboidrical crystal structure can be setempirically from measured piezoelectric characteristics.

The piezoceramic composition can be present as a single piezoceramicmaterial. The material can be a sintered or calcinated piezoceramic. Inthis case the material can be present in various crystalline phases. Forthe application of the PZT in a piezoceramic component a morphotropy ofthe PZT is for example of decisive importance. PZT is present with aspecific ratio of the proportion x of the zirconium and of theproportion of the titanium in a tetragonal and rhomboidrical crystalstructure (morphotropy).

The piezoceramic material is for example an element of a sinteredpiezoceramic body. The piezoceramic material is a monolithic PZTceramic.

A density of the piezoceramic material in the piezoceramic bodypreferably amounts to more than 96%.

In particular the piezoceramic material is a powder which is used forproducing a piezoceramic body with the composition. The powder consistsfor example of just powder particles with the piezoceramic composition.It is however also conceivable for the powder to be present as a powdermixture of various oxides which produce the composition with the general(nominal) molecular formula. For example the powder mixture consists of(1-a) lead oxide (PbO), b rare earth metal oxide (RE₂O₃), x zirconiumoxide (ZrO₂), y titanium oxide (TiO₂) and Z_(Mn), manganese oxide (MnO).A component of the powder mixture can also be a mixed oxide such aszirconium titanate ((Zr_(x)Ti_(1-x))O₂) which is accessible through ahydrothermal precipitation for example. The lead component (1-a) is setin this case such that before the beginning of a sintering a percentageexcess of lead oxide is present. This excess of lead oxideadvantageously leads to a compression of the powder at a relatively lowtemperature.

The powder is produced from the powder particles with the piezoceramiccomposition for example starting with the described powder mixture in aso-called mixed-oxide process. For the production of the powder chemicalmanufacturing methods such as the hydrothermal or sol-gel method isadvantageous, which inherently lead to homogeneous powder particles. Byexplicitly selecting the dopings based on the ion radii however, evenwhen using the low-cost mixed-oxide process, it is still possible toproduce a homogeneous doping inclusion of the rare earth metal andtransition metal from particle to particle.

In a particular embodiment the rare earth metal proportion is selectedfrom a range of 0.2 mol % to 3 mol %. The low rare earth metalproportion has a positive influence on the particle size. The lower therare earth metal proportion the greater the particle sizes that can beachieved on sintering.

In a further embodiment the overall sum of rare earth metal proportionsand transition metal proportions is less than 6 mol %. It isadvantageous if in addition to a low rare earth metal proportion thetransition metal proportion is also low. This also contributes to thefact that, even at a low sinter temperature, PZT crystals are obtainedwhich have at least the critical minimum size of 1 μm. Furthermore a lowdoping proportion means that the Curie temperature T_(c) of thepiezoceramic composition is not reduced too greatly. In particular theceramic composition has a Curie temperature T_(c) which is above 280° C.The relatively high Curie temperature leads to the piezoceramiccomposition being used at a higher temperature For example a componentwith the piezoceramic composition can be used in the engine compartmentof a motor vehicle.

As well as the level of proportions of rare earth metal and transitionmetal it is also especially advantageous for the number of differentdopings to be as low as possible. Advantageously the piezoceramiccomposition features a maximum of three different dopings. In particularRE here is a single rare earth metal and TR is selected from at most twotransition metals or TR is a single transition metal and RE is selectedfrom at most two rare earth metals. The lower number of differentdopings means that the dopings can be incorporated very homogeneouslyfrom particle to particle and within each of the particles. Thiscontributes to a very good particle growth.

In accordance with a further embodiment of the piezoceramic body withthe piezoceramic composition, the body features at least onemetallization selected from the group silver, copper and/or palladium.The piezoceramic body is manufactured in particular by joint sinteringof the piezoceramic composition and the metallization (cofiring). Themetallization can be an alloy of silver and palladium in this case. Inparticular in this embodiment the proportion of palladium is selected soas to range from 0% up to and including 30%. In this case 0%, means thatalmost no palladium is present. Preferably the proportion of palladiumis a maximum of 5%. The fact that with the aid of the piezoceramiccomposition a PZT ceramic with large PZT crystals and a high ceramicdensity is also accessible at relatively low sinter temperatures enablesmetallizations with lower melt temperatures such as silver or copper tobe sintered together with the ceramic material. In particular bysintering the piezoceramic body in a reducing sinter atmosphere it ispossible to have a low-cost copper as metallization. The option of usingsilver or a silver or silver palladium alloy with a low proportion ofpalladium as metallization means that the costs for manufacturing thesecomponents are also greatly reduced.

A further advantage as regards the piezoceramic composition is that thelikelihood of the occurrence of an interaction of the metallization andthe piezoceramic materials on sintering is reduced to a minimum. In thepiezoceramic material the number of empty positions of the A- andB-sites is minimal. During joint sintering there is only a minimumnumber of free positions available for a reaction between themetallization and the piezoceramic material. This reaction consists forexample of a diffusion of silver or copper from the metallization intothe empty positions. A suppression of this reaction allows theinteraction of the PZT with the metallization to be very easilycontrolled.

In a special embodiment the piezoceramic body exhibits a monolithicmultilayer construction in which piezoceramic layers with thepiezoceramic composition and electrode layers with metallization arearranged alternately above one another. For example the piezoceramicbody is a multilayer monolithic piezoactuator.

In particular the piezoceramic body is a component selected from thegroup actuator, bending converter, motor and/or transformer. Theactuator can for example be used for active vibration damping or formultiple injection in the motor vehicle. With multiple injection theactuator is activated several times per revolution of the engine of themotor vehicle Were a classical soft PZT to be used, because of the highinternal dissipation and the associated self-heating, this could lead tothe component overheating. With the piezoceramic composition thisproblem can be surmounted.

To produce the piezoceramic body a green body is provided in particularwith a metallization which is selected from the group silver, copperand/or palladium. The green body consists for example of green foilsstacked one above the other, provided with corresponding metallization.This green body is transferred to a piezoceramic body in monolithicmultilayer construction in a joint sinter process.

To produce the piezoceramic body the sintering is conducted inparticular in an oxidizing or reducing sinter atmosphere. By contrastwith an oxidizing sinter atmosphere, almost no oxygen is present in areducing sinter atmosphere. An oxygen partial pressure amounts to lessthan. 1.10⁻² mbar and preferably less than 1.10⁻³ mbar. This for exampleallows internal electrodes made of copper to be integrated into amultilayer piezoactuator in a joint sinter process of the piezoceramiccomposition and the copper metallization.

Preferably in this case a sinter temperature ranging from 900° C. up toand including 1100° C. is selected. Despite the low sinter temperature aceramic body with a high density is accessible. The ceramic densityamounts to 96% for example. The resulting piezoceramic body consists ofrelatively large PZT crystals. The PZT crystals obtained on sinteringexhibit, even at a low sinter temperature of 950° C. to 1100° C. forPZT, a particle diameter of much more than 1 μm.

To ensure PZT crystals with a specific minimum size a green body with aplurality of particle growth seeds can be used in this case. Theseparticle growth seeds especially feature the piezoceramic composition.The particle growth seeds can for example be produced from monolithicPZT of equivalent composition sintered at high temperature by reduction(for example grinding) with particle diameters of 1 μm and the powder,before the green body is produced, for example through foil drawing,added in a number which corresponds to the number of the PZT crystalsafter the sintering of the green body to the piezoceramic body.

In summary the invention produces the following major advantages:

-   -   The piezoceramic composition is selected so that a piezoceramic        with very large particle size is also accessible at low sinter        temperature. A final density of the piezoceramic is very high in        this case (over 96%).    -   The piezoceramic with the piezoceramic composition stands out by        virtue of high homogeneity from particle to particle and within        each particle. This is especially achieved with a pure chromium,        iron or manganese doping. The results are outstanding low-level        and high-level signal values for hard and/or soft PZTs.    -   Through the low sinter temperature a metallization with low melt        temperature can be used to produce a monolithic ceramic body by        a joint sintering of the metallization and the ceramic        composition.    -   By focusing on the maximum particle size an interaction between        the ceramic and the metallization is reduced to a minimum. This        allows defined piezoelectric characteristic values to be set and        the production of the piezoceramic to be undertaken in a stable        and reproducible way.    -   Through mixed doping of two hardener dopings a piezoceramic        component, especially a multilayer component with any given        properties between optimum soft PZT and optimum hard PZT is        accessible.

The invention will be explained in greater detail below using a numberof examples and the associated Figures. The Figures are schematic and donot represent true-to-scale illustrations

FIG. 1 a shows the dependence of the particle size on the transitionmetal proportion of a first exemplary embodiment.

FIG. 1 b shows the dependence of the dissipation factor tg δ and themechanical quality factor Q_(m) on the transition metal proportion ofthe first exemplary embodiment.

FIG. 2 a shows the dependence of the particle size on the transitionmetal proportion of a second exemplary embodiment.

FIG. 2 b shows the dependence of the dissipation factor tg δ and themechanical quality factor Q_(m) on the transition metal proportion ofthe second exemplary embodiment.

FIG. 3 shows a piezoceramic body with the piezoceramic composition.

FIG. 4 shows a method for producing the piezoceramic body.

EXEMPLARY EMBODIMENT 1

The piezoceramic composition features the following general formula:Pb_(1-a)Nd_(0, 02)Zr_(x)Ti_(y)Mn_(z)O₃. FIG. 1 a specifies thecomposition of manganese proportion Z_(Mn), in mol % and of sintertemperature depending on the particle size.

Even at a low doping with manganese the particle size increases. PZTcrystals with maximum particle size are obtained for a proportion ofmanganese which, at a sinter temperature of 1100° C., is around 1.3 mol%, that is above b_(Nd)/2 (1 mol %). The non-symmetrical doping of therare earth metal neodymium, which is contained in the compound with aneodymium proportion b_(Nd) of 2 mol % and of the transition metalmanganese, leads to maximum particle size.

FIG. 1 b shows the dependence of the dissipation factor tg δ and themechanical quality factor Q_(m) on the manganese proportion Z_(Mn), ofthe composition sintered at 1250° C. Even with a low doping withmanganese the dissipation factor tg δ falls drastically. The mechanicalquality factor Q_(m) thereby rises. The resulting piezoceramic isoutstanding by virtue of its low internal losses.

The minimum particle size necessary for a PZT ceramic is also achievedat a sinter temperature needed for a metallization of copper or silverof less than 950° C.

EXEMPLARY EMBODIMENT 2

The piezoceramic composition features the following general formula:Pb_(1-a)Nd_(0, 02)Zr_(x)Ti_(y)Fe_(z)O₃. FIG. 2 a specifies thecomposition of iron proportion Z_(Fe), in mol % and of sintertemperature, depending on the particle size.

PZT crystals with maximum particle size are obtained for a proportion ofiron which, at a sinter temperature of 1130° C., is around 3 mol % thatis above b_(Nd)(2 mol %). The non-symmetrical doping of the rare earthmetal neodymium and of the transition metal iron leads to maximumparticle size.

FIG. 2 b shows the associated dependence of the dissipation factor tg δand of the mechanical quality factor Q_(m) on the proportion of iron.Even with a greater deviation from the stoichiometric ratio of theproportion of neodymium and of iron(Z_(Fe>)3 mol %) the dissipationfactor tg δ falls considerably.

It is also true here that the minimum particle size necessary for a PZTceramic is also achieved at a sinter temperature necessary for ametallization from copper or silver of less than 950° C.

The composition in accordance with exemplary embodiment 1 is used toproduce a piezoceramic body 1 (FIG. 3). The piezoceramic body is amonolithic multilayer piezoactuator, in which ceramic layers 2 with thepiezoceramic composition and internal electrodes 3 are arrangedalternating above one another. The internal electrodes 3 are made of ametallization of a silver palladium alloy containing palladium in aproportion of 5 weight.%.

To produce the piezoactuator green foils are provided with thepiezoceramic composition (step 41, FIG. 4). To do this a powder is mixedwith the composition with an organic binder. The ceramic green foils aremolded from the slip obtained in this way. The green foils are printedwith a paste with the metallization, stacked above one another,debindered and sintered to the piezoactuator under an oxidizedatmosphere (step 42, FIG. 4). The piezoactuator is outstanding by virtueof a very good high-level signal d₃₃ coefficient at very low internallosses. The use of the piezoactuator by the electrical actuation systemdoes not result in undesired self-heating. The piezoactuator is thusalso suitable for using multiple injection systems in the engine of amotor vehicle.

1. Piezoceramic composition with the general molecular formulaPb_(1-a)RE_(b)Zr_(x)Ti_(y)TR₂O₃, in which RE is at least one rare earthmetal selected from the group europium, gadolinium, lanthanum,neodymium, praseodymium, promethium and/or samarium with a rare earthmetal proportion b, TR is at least one transition metal selected fromthe group chromium, iron and/or manganese with a transition metalvalency W_(TR) and a transition metal proportion z and The followingrelationship applies: z>b/(4−W_(TR)).
 2. Piezoceramic composition inwhich the rare earth metal proportion is selected from a range of 0.2mol % to 3 mol %.
 3. Piezoceramic composition in accordance with claim1, in which a sum of the rare earth metal proportion and of thetransition metal proportion is less than 6 mol %.
 4. Piezoceramiccomposition in accordance with claim 1, in which the RE is a single rareearth metal and TR is selected from at most two transition metals or TRis a single transition metal and RE is selected from at most two rareearth metals.
 5. Piezoceramic composition in accordance with claim 1,with a value for a mechanical quality factor Q_(m) which is selectedfrom a range 50 up to and including
 1800. 6. Piezoceramic composition inaccordance with claim 1, with a Curie-temperature T_(c) lying above 280°C.
 7. Method for producing a piezoceramic composition in accordance withone claim 1, in which a maximum particle growth of the piezoceramiccomposition is determined at a specific sinter temperature.
 8. Method inaccordance with claim 7, where the following steps are performed: a)Definition of the rare earth metal proportion b, b) Definition of thetransition metal proportion z, c) Sintering of the piezoceramiccomposition at the sinter temperature, d) Determining a particle size ofthe sintered piezoceramic composition and e) Repeating steps b) to d),with the transition metal proportion z being varied.
 9. Method inaccordance with claim 7, with the transition metal iron with an ironproportion zFe and the transition metal manganese with a manganeseproportion Z_(Mn) being used, so that the relationship toz_(Fe)+2·Z_(Mn),>b is produced and with the variation of the manganeseproportion Z_(Mn), essentially the dissipation factor tg δ of thecomposition and with the variation of the iron proportion z_(Fe),essentially the maximum value particle growth of the composition areset.
 10. Piezoceramic body with a piezoceramic composition in accordancewith claim
 1. 11. Piezoceramic body in accordance with claim 10,featuring a metallization selected from at least one of the groupsilver, copper and/or palladium.
 12. Piezoceramic body in accordancewith claim 11, in which a proportion of palladium is selected rangingfrom 0% up to an including 30%.
 13. Piezoceramic body in accordance withclaim 12, in which the proportion of palladium amounts to a maximum of5%.
 14. Piezoceramic body in accordance with claim 10, featuring amonolithic multilayer construction in which piezoceramic layers with thepiezoceramic composition and electrode layers with the metallization arearranged alternating above one another.
 15. Piezoceramic body inaccordance with claim 10, which is a component selected from the groupactuator, bending converter, motor and/or transformer.
 16. Method forproducing a piezoceramic body, with the steps: f) Provision of a greenbody with a piezoceramic composition in accordance with claim 1 and g)Sintering of the green body to the piezoceramic body.
 17. Method inaccordance with claim 16, where a green body is provided with ametallization which is selected from the group silver, copper and/orpalladium.
 18. Method in accordance with claim 16 [[or 17]], where thesintering is undertaken in an oxidizing or reducing sinter atmosphere.19. Method in accordance with one claim 16, with a sinter temperatureranging from 900° C. to 1100° C. inclusive being selected for sintering.20. Method in accordance with one claim 16, with a green body with aplurality of particle growth seeds being used with the piezoceramiccomposition.